RU2234553C1 - Abrasion-resistant cast iron - Google Patents

Abstract

FIELD: metallurgy, casting manufacture.

SUBSTANCE: invention relates to abrasion-resistant cast irons that can be used for making articles for machines and equipment subjected for abrasive and hydroabrasive abrasion. Invention proposes abrasion-resistant cast iron with ball-like graphite comprising the following components, wt.-%: carbon, 3.2-4.0; silicon, 1.4-2.5; manganese, 0.4-1.2; chrome, 7.0-10.0; nickel, 2.5-5.5; boron, 0.2-0.4; vanadium, 0.6-1.0; aluminum, 0.05-0.15; cerium, 0.05-0.20; magnesium, 0.03-0.12; calcium, 0.05-0.20, and iron, the balance. Invention provides enhancement of strength, hardness and resistance under conditions of impact-abrasive wear in retention of high indices of casting properties.

EFFECT: improved, enhanced and valuable properties of cast iron.

1 tbl

Description

The invention relates to the field of foundry, in particular to wear-resistant cast irons for the production of machine parts and equipment subjected to abrasive and hydroabrasive wear, for example, parts of ore and coal-grinding equipment, slurry pumps, slurry pipelines, etc.

Known wear-resistant cast iron containing (wt.%): Carbon - 3-3.7, silicon - 0.5-3; Manganese - 0.2-1.5; chrome 6.8-15; nickel - 4-8; phosphorus - up to 0.4; sulfur - up to 0.15; iron - the rest (see US patent No. 2662011, CL 75-128, 1953).

The disadvantages of this cast iron are: large linear shrinkage, high values of elastic modulus and coefficient of linear expansion. In connection with this, in the process of solidification and cooling, large residual casting stresses arise in the castings, which do not allow the use of this cast iron for the manufacture of metal castings from dissimilar materials, since cracks resulting from high thermal stresses during solidification of the wear-resistant layer of known cast iron to the destruction of the wear-resistant layer and obtaining low-quality bimetallic castings.

As the closest analogue, wear-resistant nodular cast iron was selected, containing, wt.%: Carbon - 3.6-3.8, silicon - 1.6-2.1, manganese - 0.5-0.7, nickel - 0.8-1.2, molybdenum - 0.5-0.6, chromium - 0.2-0.4, cerium - 0.10-0.16, copper - 0.15-0.30 and iron ( AS USSR 1560605, IPC С 22 С 37/00, publ. 04/30/1990).

However, this well-known cast iron with spherical graphite in the molten state does not provide the necessary resistance in conditions of impact-abrasive wear. The required properties of known cast iron are ensured only after complex heat treatment (isothermal hardening).

The technical result is to increase the strength, hardness and durability of cast iron compared to known cast iron under conditions of impact-abrasive wear and to maintain high casting properties, to obtain a fine-grained structure of the metal base and carbide phase with a small amount of residual austenite and spherical graphite.

To achieve a technical result, wear-resistant nodular cast iron containing carbon, silicon, manganese, chromium, nickel, cerium and iron, according to the invention additionally contains boron, aluminum, magnesium, calcium and vanadium in the following ratio, wt.%:

Carbon 3.2-4.0

Silicon 1.4-2.5

Manganese 0.4-1.2

Chrome 7.0-10.0

Nickel 2.5-5.5

Boron 0.2-0.4

Vanadium 0.6-1.0

Aluminum 0.05-0.15

Cerium 0.05-0.20

Magnesium 0.03-0.12

Calcium 0.05-0.20

Iron Else

The proposed composition of cast iron provides in the molten state obtaining a fine-grained structure of the metal base and the carbide phase with a small amount of residual austenite and spherical graphite. As a result, the strength, hardness and durability of cast iron are increased under the conditions of impact-abrasive wear and high casting properties are maintained.

The introduction of boron cast iron into the composition makes it possible to increase the proportion of fine structure carbide eutectic. The introduction of boron of less than 0.2% does not provide a sufficient amount of the carbide phase in the form of a fine-structure eutectic, which reduces the hardness of cast iron; an increase in boron content of more than 0.4% causes the release of large hypereutectic carbides, which reduces the strength characteristics of the metal.

The addition of vanadium to the composition of the proposed cast iron contributes to the depletion of austenite by carbon due to the formation of vanadium carbides, due to which the temperature of martensitic transformation increases, part of the residual austenite turns into austenite, while the fraction of residual austenite decreases and, accordingly, the strength, hardness and wear resistance of cast iron increases.

The introduction of vanadium in the composition of cast iron less than 0.6% does not provide the allocation of a sufficient amount of vanadium carbides, does not change the fraction of residual austenite, as a result of which the hardness of cast iron does not increase. An increase in the amount of vanadium over 1% prevents the formation of free carbon in the form of spherical inclusions of graphite and increases the tendency of cast iron to crack formation.

Smelting of wear-resistant cast iron of the proposed composition is as follows.

Cast iron is melted in induction or electric arc furnaces using standard charge materials. Alloying elements - nickel, chromium and vanadium are introduced into the metal plant. After the charge is melted and the cast iron is overheated to 1450-1500 ° С, silicon and manganese are introduced into the melt mirror in the form of 75% ferrosilicon and 60% ferromanganese. Then aluminum and calcium are added (in the form of 20% silicocalcium). Magnesium in the composition of the spheroidizing additive, as well as cerium and boron in the form of ferrocerium and ferroboron, are introduced to the bottom of the casting ladle before the liquid metal is discharged from the furnace.

The chemical composition, structure, mechanical properties and relative wear resistance of the proposed cast iron are shown in the table.

The table shows that the proposed cast iron, due to its higher strength (850-1050 MPa) and hardness (60-63 HRC), as well as due to less residual austenite (10-15%) has higher wear resistance than the prototype .

Temporary iron flexural resistance (σ _mfd) were determined on cylindrical specimens (⌀25 × 200 mm) cast in quartz tubes, molded into sand-clay mixture.

Wear resistance under conditions of impact-abrasive wear was determined by the weight loss of the samples after 12 test cycles lasting 25 minutes each. Impact-abrasive wear tests were carried out at the laboratory planetary mill of the TsNIITMASH design. As an abrasive, quartz sand of a certain grain size was used. The standard was taken to wear samples made of steel 20.

Compared with the prototype, cast iron of the proposed composition has a low tendency to crack formation and can be used for the manufacture of both monometallic and bimetallic wear-resistant parts.

The use of the proposed wear-resistant cast iron for castings, for example, bandages and grinding elements of medium-speed coal-grinding mills, eliminates casting defects by hot cracks and significantly (by 50-80%) increases the service life of parts in operation under shock-abrasive wear.

The results are given in the table.

Claims (1)

Wear-resistant nodular cast iron, containing carbon, silicon, manganese, chromium, nickel, cerium and iron, characterized in that it additionally contains boron, aluminum, magnesium, calcium and vanadium in the following ratio, wt.%: Carbon 3.2 - 4.0 Silicon 1.4 - 2.5 Manganese 0.4 - 1.2 Chrome 7.0 - 10.0 Nickel 2.5 - 5.5 Boron 0.2 - 0.4 Vanadium 0.6 - 1.0 Aluminum 0.05 - 0.15 Cerium 0.05 - 0.20 Magnesium 0.03 - 0.12 Calcium 0.05 - 0.20 Iron Else